In the drilling and production of oil and gas wells, downhole tools are located on work strings and run into well bores to perform various tasks within the well. Due to the cylindrical nature of the well bore together with the tubing used in the well, these tools typical comprise a cylindrical body located in the work string and annular or part annular components located on or around the body. When run in the well, these components provide for operation of the tool and a desired task is performed in the well.
In constructing the downhole tools, one example of a component is an annular sleeve. Relative movement between the sleeve and body operates the tool. The sleeve is typically formed as two semi-cylindrical portions held together along the two longitudinally arranged mating surfaces. The clamping of the portions is achieved by forming a hole through the portions at the mating surfaces. Typically the hole is perpendicular to the mating surface. A recess is formed at each end of the hole to allow a nut and bolt to be used as a fastener to clamp the portions together.
A disadvantage of this type of fixing is that the bolts are not properly constrained and consequently the nuts and/or bolts are easily lost and the assembled tool can be tampered with as the fastener is easily accessible. This can result in some tools being used with missing or loose fasteners which can result in failure of the tool downhole.
To reduce the number of fastenings, some sleeves are formed with the portions hinged so that fastenings are only required at a single mating surface. However, the single row of fasteners produce a sleeve with asymmetric loading and the fasteners can still be tampered with.
To prevent tampering with the fasteners it is known to use fasteners which can only be operated by a unique or specialist implement. Such fasteners have the disadvantage that the implement must be carried beside the tool for times when release of the fasteners is required. This is very inconvenient for tools which are assembled onshore and transported offshore for use.
A further example of an annular component is a scraper or brush. On a downhole cleaning tool there will be rows of brushes or scrapers generally biaised outwards to contact the wall of the liner or casing of the well. Movement of the brushes/scrapers over the wall clean debris and other detritus from the wall. On a typical tool, such as that illustrated in U.S. Pat. No. 4,648,447, the body is made up in sections which are threaded together. The cleaning elements, scrapers in this case, are slid over a section of the body to locate under lips or recesses and hold them in position. The second part of the body is then connected to the first and further lips retain an opposite end of the elements.
These tools have a major disadvantage in that the work string must be disconnected and reconnected everytime the cleaning elements need to be replaced. This is both time consuming and requires skilled engineers to ensure the biaised elements are correctly positioned when the tool is re-assembled.
Another method of retaining the cleaning elements without disconnecting the work string is to locate an annular sleeve over the ends of the elements. This is illustrated in U.S. Pat. No. 5,711,046. However, the annular sleeves have the same disadvantages as discussed hereinbefore.